1. this shouldn't be bold 2. Personally, I think this would be Euclid, however, I see why it would be Keter

is to be kept in a 13m x 13m x 5m cell

Why must the cell be so specific? Will it escape otherwise? "Standard humanoid containment" works fine.
That brings me to the rest of the containment. Most of these things are redundant, or obvious. Either way, they are unnecessary. Things like:

Always run tests of SCP-XXXX cell to make sure the security protocols are foolproof.

are something that the Foundation would already do, so they wouldn't be in the procedures. They are Special containment procedures, they have to be what would change their storage from any other object.

SCP-XXXX was found in █████████ U.S.A. It was found eating insects and doing typical arachnid behaviour.

1. discovery goes at the end of the description 2. what is typical arachnid behavior? With so many species of arachnid, it is hard to tell.

The rest of the description can be expanded upon, take each anomalous property (in logical groups) and put them into their own paragraph.

Concept: It's weak. All it is, is a generic monster. Modern SCiPs often have stories woven into the document. I suggest that in the future, you go to the Brainstorming forum to develop your ideas before writing.

UnknownCommander, instead of posting multiple comments in succession, please edit your previous post using the "edit" function under the "options" tab to the lower right of every comment. That prevents spam buildup, and it's in the rules.

Furthermore:

About the specific cell size, I plan to add the fact that it has earned privileges to make webs in the cell as long as it won't attempt to cover the cameras

Sure, but there's no reason to require that those measurements must be used. What if the cell is 14 meters to one side? (For the record, that's a pretty big cell.) You can have a lower bound for sizing, but an exact specific doesn't usually make sense to require.

This has nothing to do with in-universe protocol. The Foundation has a lot of things to contain, and requiring specifics like this presents an additional inconvenience for the engineers who are designing facilities to accommodate these anomalies.

Yes. But you as the author are different from the person in the fictional Foundation who would be writing the SCP article. We expect SCP articles to sound like the work of professional scientists, not kids playing the game or something.

It's not a good draft. Most obviously, the clinical tone and grammar needs a lot of work. Like the following:

an inordinate amount of monitors must be in SCP-XXXXs cell at all times

Here you've forgotten to capitalize "an", as well as missed the apostrophe in "SCP-XXXXs", which isn't even mentioning the clinical tone errors.

What grade are you currently in at school? Most successful SCP authors have at least some college-level writing experience, since clinical tone is typically covered in college. If you haven’t encountered clinical tone or writing analytical essays in school yet, it can be hard to write an article meant to sound like the work of a professional scientist.

Sorry for the mistakes. But I WAS writing late at night so I might make some spelling errors sometimes. And I am dozing off so I just no care about grammar and spelling up to this point mostly. I get sleep now

I recommend taking each paragraph and pasting each into Grammarly or a similar website. it helps smooths out common errors, and spelling mistakes! Furthermore, try to sound professional when writing out a SCP document, think about it like real life. You would want the clarity, and description to be on point so there is no(if possible) questions about the current viable information.